This invention relates to hand operated power tools of the type for reciprocating saw blades and the like. Such tools are electrically operated and characterized by a driving head that reciprocates a ram rod to which a saw blade or the like is attached as by means of a set screw or chuck. A feature of these power saw tools is a shoe that slidably engages and limits the penetration of the saw blade into the workpiece. A heavy duty power saw tool of the type under consideration is shown in FIG. 1 of the drawings herein, with the aforesaid guide shoe removed and replaced by the file adapter of the present invention. Also, a common hand file (modified) replaces a saw blade for which this particular power tool is designed.
Heretofore, slender elongated saw blades of thin cross section (0.040xe2x80x3 to 0.050xe2x80x3), and sander attachments, have been operated by such power tools, so as to reciprocate against and through the workpiece. Various guide mechanisms have been associated with the controlling shoe to back up the saw blade as it is pressed against the workpiece. A characteristic of these power saw tools is the relatively short stroke of the saw blade which too is relatively short and not as lengthy as a hand saw would be. In other words, the power tools of the prior art have not been conducive to the adaption thereto of lengthy hand files.
It is the common hand file with which this invention is particularly concerned, and it is to be understood that there are various special files to which the adapter system of the present invention is to be applied. The files with which this invention is concerned are elongated bars with a surface upon which teeth are formed to engage and cut material from a workpiece. The cross sectional configuration of these bars varies in order to present a toothed surface, and the coarseness and number of teeth is as circumstances require. For example, files can be flat, round, half-round, triangular or rectangular, and the tooth configuration coarse cut, bastard cut, single cut, double cut, etc. There are also rasp files with an arrangement of round cupped teeth. It is to be understood, therefore, that this invention relates to all files, a characteristic of which is a body of hardened steel having a base end with an annealed tang of tapered configuration extending from a base end thereof. A full sized common file has an active toothed face which can be nine inches long and seven-eighths inch wide, with a base and tang approximately three inches long extending therefrom (these dimensions are variable). It is this common hand file with which this invention is particularly concerned, and an objective of this invention to modify such a file and thereby adapt it to a chuck of a power saw tool.
Hand filing involves manipulative skills. That is, the teeth are formed so as to cut only during a forward pushing motion during which downward pressure against the workpiece must be applied. Too little pressure especially on hard materials tends to dull the teeth quickly. And too much pressure tends to clog the teeth and break them off. Accordingly, pressure against the workpiece must be applied in order to render a file effective. It is to this end that an object of this invention is to provide a power saw tool adapter for applying work pressure to the back side of a file coupled to the reciprocating chuck portion of the tool. In accordance with this invention, the work pressure is applied to the base-tang end portion of the file, the work pressure being shared by the chuck and ram-rod of the power tool.
In the course of rough shaping a workpiece with the power saw tool file adapter of this invention, lateral pressures are applied to the file that is anchored to the reciprocating chuck of the tool. In practice, the active toothed portion of the file extends four or five times its base length, forming a lever arm that could destroy the coupled attachment of the file to the tool chuck. One objective of this invention is to eliminate bending stress from the file-to-chuck connection, by means of a fixedly positioned guide roller operating as a resistance member in a guideway formed in the back side of the file base.
One embodiment of this invention provides a file adapter that replaces the prior art shoe of power saw tools. The adapter provides (1) a resistance for the application of downward work pressure, and (2) a double resistance for side to side reception to lateral work pressures; all of which prevents destructive forces from being applied to the file-to-chuck connection. Accordingly, a second class lever is involved in any situation, the chuck of the power tool being the fulcrum, the guide roller being the resistance, and the extended file being the forceful lever arm.
As mentioned, the teeth on a file are designed to cut only in a forward pushing motion against the workpiece. Dragging the file across the workpiece in a reverse direction can dull the teeth. One embodiment of the invention provides a file adapter that prevents dragging the file backwards across the workpiece during each reverse stroke of the reciprocating file.
Since the file is reciprocated forcefully at high speed by the power tool, there is a need to ensure that the file is not ejected from the adapter if the file-to-chuck attachment becomes loosened or the file breaks, for example. One embodiment of the adapter provides a safety feature that prevents the file from being ejected under these circumstances.
This file adapter system for electrical power tools is especially suited for incorporation in a xe2x80x9cSAWZALLxe2x80x9d power operated saw manufactured by Milwaukee Tool Corp. and disclosed in U.S. Pat. No. 5,855,070 issued Jan. 5, 1999. (xe2x80x9cSAWZALLxe2x80x9d is a registered trademark of Milwaukee Tool Corp.) The file adapter of this invention replaces the pivotally attached shoe thereof in order to operate a file in place of a saw. The Milwaukee ""070 patent power tool features the adjustable shoe that pivotally engages the workpiece, whereas the present invention adapter does not engage the workpiece but rather engages and controls the work cutter in the form of a file. The Milwaukee ""070 patent power tool is a heavy duty tool used generally in a horizontal position and manipulated into any other convenient position, and is characterized by its longitudinally disposed reciprocal axis, there being a motor and drive head intermediate a hand grip and functional working end. The work engagement shoe is essentially an attachment and there is an adjustable lock to receive the shoe attachment at three extended positions. A feature of the Milwaukee ""070 power tool is the two-jaw chuck for coupling the flat faced end portion of a saw blade or the like to the operational end of the reciprocating ram-rod. The ram-rod is rotatably guided so as to maintain the flat base of the saw blade in a vertical plane coincidental with the reciprocal axis. The saw blade cantilevers from the chuck when coupled thereto.
Briefly, the file adapter of this invention enables a file to cantilever from the aforesaid power saw tool chuck without subjecting the coupled attachment to damaging bending stresses. The file-to-chuck attachment is essentially a hinge and therefore bending moments can be critically high. However, by restricting the file-to-chuck attachment so as to function as the fulcrum of a second class lever, bending stresses are virtually eliminated, since the function of the resistance roller herein provided prevents upward and side movement of the file at a position substantially removed from the fulcrum. In practice the fulcrum shifts approximately 2.25 inch and 3.50 inch from the resistance roller as a result of reciprocal motion. This provides a variable lever that is sufficient to withstand the downward and lateral operational loads normally applied.
In carrying out one embodiment of this invention, the annealed base and tongue portion of the file is modified, as by forging a vertically disposed coupling plate thereof, or by integrally fastening such a plate to the base of the file. A feature of the file modification is a roller guideway in the face thereof opposite the cutting face of the file. In practice, a small portion of the cutting face may be sacrificed to accommodate the roller guideway, at either or both sides of the file.
The file adapter employs the support and locking adjustment of the Milwaukee ""070 patent power tool and provides a fixedly placed resistance roller support overlying the base portion of the file to engage in the roller guideway therein.
In another embodiment of the invention, the file adapter includes a hinged bracket which allows the resistance contact with the file to shift back and forth during the file""s reciprocating motion. This hinged adapter releases a downward force on the file during each return stroke of the reciprocating file to prevent dragging the file backwards across the workpiece, thereby preventing undue wear.
Another embodiment of the invention provides a safety feature that prevents the file from being ejected from the adapter if the file is dislodged from the file-to-chuck attachment, or if the file breaks. In this embodiment a specially designed file having protruding stops is inserted through a widened portion of the adapter and then locked in the chuck adjacent a different narrowed region of the adapter in alignment with the operative position of the file. During use, if the file is dislodged during its reciprocating motion, the stops on the file engage the narrowed portion of the adapter which captures the file inside the adapter to prevent ejecting it from the power tool.